package com.SuanFa.test;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.text.DecimalFormat;
import java.util.Scanner;

public class test3 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double d = sc.nextDouble();
        double sqrt = Math.sqrt(5);
        double d1 = (1 + sqrt) / 2.0;
        double d2 = (1 - sqrt) / 2.0;
        double pow = Math.pow(d1, d);
        double pow1 = Math.pow(d2, d);
//        DecimalFormat df = new DecimalFormat("0.00");
//        System.out.printf(df.format((pow-pow1)/sqrt));
        BigDecimal db=new BigDecimal((pow-pow1)/sqrt);
        BigDecimal bigDecimal = db.setScale(2, RoundingMode.HALF_UP);
        System.out.println(bigDecimal);
    }
}
